In preliminary testing, a group of investigators at the University of Colorado found that D-xylose absorption was suppressed when given with their modified PABA test. Our group has developed a kinetic model of D-xylose absorption that can characterize D-xylose absorption into two rate constants Ka, rate of absorption, reflecting mucosal function, and Ko, rate of nonabsorptive loss, reflecting D-xylose lost in the GI tract.